Shaft shear in a gas turbine engine is a potentially catastrophic condition where, for example, the low pressure shaft has broken, the shaft portions continue rotating and the aft portion is driven aftward due to gas flow over the low pressure turbine. Rapid engine shutdown is required and specifically the fuel supply to the engine must be terminated immediately to prevent the resulting unloaded turbine from accelerating up to the turbine burst speed.
To detect shaft shear conditions by, for example, subsequent axial motion of the shaft to the aft position, sensors or probes are positioned in the engine adjacent the rear end of the shaft. When the shaft collides with the sensors, electronic controls generate a signal that results in fuel supply termination and engine shutdown.
Since the shaft shear condition and complete loss of engine operation are potentially catastrophic to the engine and aircraft, multiple sensors are installed to provide the necessary redundancy and reliability.
However any electronic sensor can malfunction due to internal damage, or the circuit connected to the sensor may be faulty. The sensors are housed in the engine core surrounded by the hot gas path, subjected to vibration and adjacent rotary components operating at high speed.
Therefore there is a need for reliable sensor operation which can properly detect shaft shear while minimizing false alarms.
Features that distinguish the present disclosure from the background art will be apparent from review of the disclosure, drawings and description of the disclosure presented below.